When we get to a boss things change a little bit because now you might only have one enemy to deal with.
I wait for my group to be close or in the boss area and I start off with a Provoke. I use this sparingly as a Tank because you often don’t need to use it but it can be helpful to force an enemy to target you, especially when you start doing 8 person trials in the future.
On a boss you want to maintain doing your damage combo rotation and this consists of Fast Blade followed by Riot Blade, now is also a good time to use Fight or Flight which increases your damage, you can use this during add pulls too if you’re not too busy.
I keep Low Blow on my bar because this works quite well for most bosses at the start when they do an AoE or channelled attack you can hit Low Blow to stun them and prevent them from doing it.
If you are on a boss fight where adds spawn, sometimes you’re not expected to aggro them all but the best way to do so is by using your enemy list and either Shield Lob or Provoke them to attack you.
Bosses are a bit different than adds pulls because you don’t want to waste all of your mitigation skills. There are things known as Tank Busters where you gain a red indicator around your character, this is telling you that a huge hit is about to happen and so you need to pop your mitigation skills at this point. Generally I will use Reprisal on cooldown on bosses and save my Rampart for Tank busters.
Outside of this you simply need to learn and play mechanics, if you can’t Low Blow the enemy to stop an AoE attack then you walk out of it!